Wave guide impedance transformer



Oct. 20, 1953 w. W,`HANSEN ET AL Y 2,656,515

l WAVE GUIDE IMPEDANCE TRANSFORMER Original Filed March 31, 1942 EF1/lg.j.

2 ze. z3 fg 20 B 0L VE D. R055, vicar/wx B m .THE/R ATTORNEY PatentedOct. 20, 1953 UNITED STATES PATENT OFFICE WAVE GUIDE IMPEDANCETRANSFORMER Application May 5, 1945, Serial No. 592,092, now Patent No.2,531,437, dated November 28, 1950, which is a division of applicationSerial No. 437,004, March 31, 1942, now Patent No.

2,433,368, dated December 30, 1947.

Divided and this application April 6, 1950, Serial No.

14 Claims. l

The present invention relates to the art including impedance matchingand transforming devices especially adapted for use in systems utilizinghigh frequency electromagnetic energy conducted in wave guides.

The present application constitutes a division of prior copendingapplication Serial No. 592,092, filed May `5, 1945, which became anissued Patent No. 2,531,437, on November 28, 1950, and was, in turn, adivision of prior copending application Serial No. 437,004, filed March3l, 1942, which became an issued Patent No. 2,433,368, on December 30,1947, for Wave Guide Construction.

In transferring energy from one high frequency device to another, it iswell known that the impedances thereof must be properly matched in orderto avoid the production of standing waves, with their attendant increasein losses and decrease in the energy transmitting capacity of thesystem. In addition, for greater eiciency of power transfer, itis knownthat the impedance of a load device must be properly matched to that ofthe high frequency source.

The present invention is directed toward the provision of improvedimpedance transforming devices which are adapted to transform andimpedance connected at one end to a different value at the other end ofsuch a transforming device, whereby this transformed impedance may bematched to a load or other impedance connected at such other end.

Accordingly, it is an object of the present invention to provideimproved impedance transformers for transforming a given impedance intoa desired impedance.

Another object of the present invention is to provide an improvedadjustable impedance transformer for use in the system having a maximumease of adjustment and range of impedance transformation.

Other objects and advantages will become apparent from the followingspecification and drawings, in which Fig. 1 shows a longitudinalsectional view of a Wave guide incorporating an impedance transformeraccording to the present invention.

Figs. 2 and 3 show corresponding longitudinal sectional views ofmodified forms of a xed impedance transformer.

Fig. 4 shows a longitudinal sectional view of an adjustable wave guideimpedance transformer.

The present invention is useful especially in the connection between ahigh frequency source and a radiating wave guide, such as shown in saidPatent No. 2,433,368. Such radiating wave (Cl. S33-33) guides in generalrequire impedance matching devices to match them to the wave guidesthrough which the input energy flows. Such devices form the presentinvention.

Fig. 1 shows a rectangular radiating wave guide 20 in section, whoseradiating slot begins at the point I9 and which is attached to arectangular wave guide 2| whose cross-section is equal to that of theradiating guide. Preferably equal height conducting plugs 22, '22 areattached to opposite surfaces of the wave guide 2d perpendicular to theside containing the slot. The distance between these wave guide surfacesis h1 and is the minor cross-sectional dimension of the guide, while thedistance between the opposed faces of the plugs 22 and 22 is h2. Thelength of the plugs 22, 22 is approximately a quarter wavelength of theoperating frequency or an odd multiple thereof, as measured in the guide263. The proper position of the plugs .22, 22 along the longitudinalaxis of guide 2l may be determined by measuring the standing wave ratioV max V min in the guide 2| as a function of distance along this guide.Here V max V min is the ratio of the magnitude of the voltage antinodesto the voltage nodes in the guide 2| before the plugs are in place. Theplugs 22, 22' are then inserted and fastened so that one edge of theplugs, at 23, 23', is at a voltage nodal 'point for the standing wavefound in the guide. The thickness of the plugs is determined by thestanding wave ratio V max V min and the height h1 of the guide, asexpressed by the relation:

2, a new nodal point 24, 24 being `found to determine the position ofsmaller plugs 25, 25', the plugs 25, 25 also being approximately aquarterwave long in the guide 2l.

The matching sections need not be reentrant, as in Figs. 1 and 2, butmay enlarge the guide in one or two oppositely spaced enlargements, asat 26, 26 in Fig. 3. Ii the larger dimension is still defined as h1, itwill here refer to the height of the enlarged portion 2S, 25 while thesmaller distance h2 will refer to the height of the guide 2l itself.With these deinitions, the size of the enlarged portion 2G, 2S' is againdetermined by Equation l. The edgesl 30, 39 are now placed at thevoltage anti-node nearest the slot, each enlargement 25, 26 beingapproximately a quarter-wave long in the guide 2i. This type oftransformer may be preferred to the reentrant type, as it avoids highelectric fields and lessens the likelihood of arch-overs at high powerlevels.

While the edges 2.3, 23 of the plugs 22, 22 of Fig. l and the edges Se,Se' of the enlarged section 26, 2S of 1Eig. 3 are described as beingpositioned at a voltage nodal point and voltage antinodal pointrespectively, it will be understood that these edges could equally wellbe dened as to position in terms of current along the guide, the edges'23, 23' being positioned at a current maximum and the edges 3c, 3cbeing positioned at a current minimum. Thus, both edges 23, 23 and 3G,39 may be described as being positioned at a point of maximum amplitudeof one of the two electrical quantities, i. e., voltage or current.

The devices of Figs. l and 3 may be made adjustable in the manner shownin Fig. 4. A slidable guide 2'! with ends preferably tapered over adistance large relative to one-half-wavelength in the guide 2 i, as at23, 2S (shown oreshortened here for convenience of illustration) ismounted to slide in the end of the excited `wave guide 3i and thenon-radiating guide 2i feeding directly into the radiating guide it orany other device, as desired. Projecting preferably at right angles toguide 2l and mounted thereon is a rectangular tube 33 in which aconducting rectangular piston @il may be positioned by means of knob 35.Piston 34 is substantially a quarter-wavelength long as measured in theguide 2i or Si in the direction of energy flow, and is substantially asdeep as guide 2l. 'he procedure in adjusting the transformer may besimilar to that for adjusting or selecting the location of thetransformer of Figs. l, 2 or 3. If desired, two plugs similar to 35 butat opposite sides of section 2i may be used, to more closely approachthe type of transformer shown in Figs. 1 and 3.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madeWithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A means of matching impedances coupled to a portion of a rectangularconducting wave guide excited by electromagnetic Waves, said guidehaving a pair of oppositely positioned plugs of substantially equalthickness and of a length approximately an odd multiple including one ofa quarter Wavelength of the exciting waves, corresponding edges of saidplugs being placed at a voltage nodal point for said waves and thedistance Vbetween the plugs being equal to the `height of the guidemultiplied by the ratio of amplitudes of the voltage nodes to thevoltage loops.

2. A means of matching impedances coupled to a portion of a rectangularconducting Wave guide excited by electromagnetic Waves, said guidehaving a conductive plug therein of a length approximately an oddmultiple including one of a quarter Wavelength of the exciting waves, anedge of said plug being positioned at a voltage nodal point for saidwaves and the thickness of said plug being equal to the height of theguide mutiplied by the factor unity minus the ratio of amplitudes of thevoltage nodes to the voltage loops.

3. A means of matching impedances coupled to a wave guide of rectangularsection excited by electromagnetic Waves, comprising an enlarged widthsection of said guide, said enlarged Width section being of lengthapproximately an odd multiple including one of a quarter Wavelength ofthe exciting Waves, the height of said enlarged section being equal tothe height of said Wave guide multiplied by the ratio of amplitudes ofthe voltage loops to the voltage nodes for said waves.

4. Apparatus as in claim 3 wherein one end of said enlarged section ispositioned in said wave guide at a voltage nodal point for said waves.

5. A means for matching impedances coupled to a portion of a rectangularconducting wave guide excited by electromagnetic Waves, said guidehaving a pair of oppositely positioned plugs of a length approximatelyan odd multiple including one of a quarter Wavelength of the excitingwaves, the distance between the plugs being equal to the height of theguide multiplied by the ratio of the amplitudes of the voltage nodes tothe voltage loops.

6. Apparatus as in claim 5 wherein said plugs are of equal thickness.

'7. A means of matching impedances coupled to a portion of a rectangularconducting wave guide excited by electromagnetic waves, said guidehaving a conductive plug therein of a length approximately an oddmultiple including one of a quarter wavelength of the exciting Waves,the thickness of said plug being equal to the height of the guidemultiplied by the factor unity minus the ratio of amplitudes of the voltage nodes to the voltage loops.

8. A means of matching iinpedances coupled to a portion of a rectangularconducting wave guide excited by electromagnetic waves, said guidehaving a plurality of pairs of oppositely positioned plugs each of alength approximately an odd multiple including one of a quarterwavelength of the exciting Waves, corresponding edges of said pairs ofplugs being placed at a voltage nodal point for said waves, and thedistance between the plugs of each of said pairs being equal to theheight of the guide multiplied by the ratio of amplitudes of the voltagenodes to the voltage loops.

9. An adjustable impedance transformer in a Wave guide, comprising meansforming a quarter-Wave section of Wave guide having adjustablecross-sectional dimensions, and means for adjusting the position of saidsection axially relative to the remaining portions of said wave guide.

l0. An adjustable impedance transformer for use with a wave guideexcited by electromagnetic waves comprising a section of Wave guideWhose length equals an odd multiple including one of a quarterwavelength of the exciting waves, means for adjusting thecross-sectional dimensions of said Wave guide section, and means foradjusting the longitudinal position of said waveguide section relativeto said wave guide.

11. Microwave transmission apparatus comprising a hollow rectangularWave guide section having predetermined major and minor crosssectionaldimensions, and at least one conductive plug positioned in the guide,the plug having a length extending along the longitudinal axis of theguide of approximately an odd multiple including a quarter wave lengthof the exciting wave, a transverse edge of the plug being positioned ata voltage nodal point of the exciting Wave, the plug providing a reducedminor crosssectional dimension equal to the normal minor cross-sectionaldimension multiplied by the ratio of the amplitudes of the voltage nodesto the voltage loops.

12. Microwave transmission apparatus comprising a rectangular wave guidesection having predetermined major and minor cross-sectional dimensions,and at least one conductive plug positioned in the guide and providing areduced minor cross-sectional dimension, the plug having a lengthextending along the longitudinal axis of the guide of approximately anodd multiple including a quarter wavelength of the exciting wave, atransverse edge of the plug being positioned at a voltage nodal point ofthe exciting wave.

13. Microwave transmission apparatus for matching a load impedance to arectangular wave guide excited by electromagnetic waves, said apparatuscomprising a section of rectangular Wave guide having major and minorcross-sectional dimensions, a portion of said section having a minorcross-sectional dimension dierent than the minor cross-sectionaldimension of the remainder of the section, said portion being of alength approximately an odd multiple including one of a quarterwavelength of the exciting waves, the larger minor cross-sectionaldimension along said section being equal to the smaller minorcross-sectional dimension along said section multiplied by the ratio ofamplitudes of the voltage loops to the voltage nodes for said waves.

14. Microwave transmission apparatus for matching a load impedance to arectangular wave guide excited by electromagnetic waves of apredetermined frequency and wavelength, said apparatus comprising atleast three tandem sections of said rectangular wave guide fortransmission of the energy from the source to the load, the firstsection having major and minor cross-sectional dimensions substantiallyequal to the respective major and minor cross-sectional dimensions ofthe third section, and the intermediate section being of an electricallength approximately an odd multiple including one of a quarterwavelength of the exciting energy, the junction of said intermediatesection and said third section being situated at a position of themaximum amplitude of one of the two electrical quantities includingvoltage and current along the wave guide, and the minor cross-sectionaldimension of said intermediate section being related to the minorcross-sectional dimension of said third section in the ratio of theamplitude of the Voltage at said junction to the amplitude of thevoltage in said third section at a distance from said junction of onequarter wave guide wavelength therein.

OLIVE D. ROSS,

Eecutrix of the estate of William W. Hansen,

deceased.

MONTGOMERY H. JOHNSON.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 2,106,768 Southworth Feb. 1, 1938 2,106,769 Southworth Feb. 1,1938 2,125,597 White Aug. 2, 1938 2,129,669 Bowen Sept. 13, 19382,405,174 Alford Aug. 6, 1946 2,407,911 Tonks Sept. 17, 1946 2,408,745Espley Oct. 8, 1946

